The invention relates to a machine tool having a machine frame and a workpiece table.
In the case of machine tools of the type stated at the outset, deformations and, consequently, errors in the machine tool geometry can occur because of differing workpiece loads and machining loads of the workpiece table. These geometry errors can reduce the accuracy of the workpiece. The requirement for highly accurate workpieces and/or greater automation and/or increased productivity makes it necessary to eliminate, or at least reduce these geometry errors. Alternatively, or additionally, unwanted vibrations can occur during machining. These vibrations affect the machining throughput of the machine tool and reduce the accuracy and the surface quality of the workpieces.
Known from DE 10 2006 049 867 A1 is a machine tool having a workpiece clamping device on a workpiece table, for the purpose of clamping a workpiece. The workpiece clamping device can be moved by means of piezo actuators, in order to reduce vibrations occurring during the machining operation. For this purpose, on the workpiece table there is a so-called piezo table, realized in the manner of a frame, the workpiece clamping device being located within the frame. A piezo actuator serves to position the workpiece clamping device in respect of height, and four further piezo actuators position the workpiece clamping device relative to the frame. In addition to the active mounting by means of the piezo actuators, passive mounting is provided, which is realized in that a spring-loaded strut acts in parallel with each piezo actuator. In order to effect positioning movements of the piezo actuators, a feedback control is provided, which registers errors in the position of the workpiece clamping device in relation to the piezo table mounted in a fixed manner on the workpiece table and corrects these errors in order to prevent vibrations. The result of all of that is that the known machine tool is provided with a piezo device for positioning a workpiece clamping device in order to prevent vibrations. However, this does not affect the machine-tool geometry errors mentioned at the outset. The application possibilities for such a known arrangement are therefore limited and, depending on the size and weight of the workpiece, require corresponding embodiments of the piezo table and piezo actuators, in addition to spring-loaded struts.
It is an object of the invention to create a machine tool, of the type mentioned at the outset, that can be used to produce highly accurate workpieces having a first-class surface quality, without the need for additional devices adapted to the workpieces.